Method of and apparatus for forming interconnection

ABSTRACT

The present invention relates particularly to a method of and an apparatus for forming a fine interconnection in a highly integrated circuit formed on a semiconductor substrate. The method has the steps of preparing a substrate having fine recesses formed in a surface thereof, dispersing ultrafine particles made at least partly of a metal in a predetermined solvent, producing an ultrafine particle dispersed liquid, supplying the ultrafine particle dispersed liquid to the fine recesses of the substrate, heating the substrate to melt and bond the metal, and chemical mechanical polishing the surface of the substrate to remove an excessively attached metal therefrom. According to the present invention, it is possible to stably deposit an interconnection metal of good quality using an inexpensive material.

REFERENCE TO RELATED APPLICATIONS

The present application is the national stage under 35 U.S.C. §371 ofinternational application PCT/JP00/07110, filed Oct. 13, 2000 whichdesignated the United States, and which application was not published inthe English language.

TECHNICAL FIELD

The present invention relates to a method of and an apparatus forforming an interconnection, and more particularly to a method of and anapparatus for forming a fine interconnection in a highly integratedcircuit formed on a semiconductor substrate such as a semiconductorwafer or the like.

BACKGROUND ART

Aluminum or aluminum alloy has generally been used as a material forforming interconnection circuits on semiconductor substrates. It hasbeen customary to grow a film of the material according to a processsuch as sputtering, CVD, or the like and then produce a pattern in thefilm according to etching or the like. As the level of circuitintegration increases in recent years, there is a demand for the usageof silver, copper or its alloy, which has a higher conductivity, as aninterconnection material. Since it is difficult to etch these materials,it has been proposed to immerse a substrate having interconnectionpattern trenches therein in a plating liquid and perform electrolytic orelectroless plating on the substrate to embed the trenches with silver,copper or its alloy.

However, while the plating processes are an inexpensive and highlytechnically accomplished technology, the electrolytic plating process iscapable of growing a film only on an electrically conductive material,whereas the electroless plating process suffers a problem in thatsubstances contained in the plating liquid affect the naturalenvironment and the working environment. Accordingly, there has been astrong need for the development of a metal interconnection technology asa substitute for the plating processes.

DISCLOSURE OF INVENTION

The present invention has been made in view of the foregoing problemsand demand. It is an object of the present invention to provide a methodof and an apparatus for forming an interconnection by stably depositingan interconnection metal of good quality as a substitute for theconventional plating processes.

According to an invention described in claim 1, there is provided amethod of forming an interconnection, comprising the steps of preparinga substrate having fine recesses formed in a surface thereof, dispersingultrafine particles made at least partly of a metal in a predeterminedsolvent, producing an ultrafine particle dispersed liquid, supplying theultrafine particle dispersed liquid to the fine recesses of thesubstrate, heating the substrate to melt and bond the metal, andchemical mechanical polishing the surface of the substrate to remove anexcessively attached metal therefrom.

With the above arrangement, it is possible to easily forminterconnections according to so-called single and dual damasceneprocesses.

The ultrafine particle dispersed liquid may be placed in a container,providing a liquid reservoir, and the substrate may be immersed in theliquid reservoir to supply the ultrafine particle dispersed liquid toonly the fine recesses of the substrate. Alternatively, the ultrafineparticle dispersed liquid may be supplied to the fine recesses of thesubstrate by being coated or sprayed in the fine recesses of thesubstrate and/or on areas surrounding the fine recesses. Furthermore,the ultrafine particle dispersed liquid may be coated by a spin coatingprocess.

According to an invention described in claim 2, the method according toclaim 1 comprises the step of evaporating the solvent between the stepof supplying the ultrafine particle dispersed liquid to the finerecesses of the substrate and the step of heating the substrate to meltand bond the metal.

According to an invention described in claim 3, in the method accordingto claim 1 or 2, each of the ultrafine particles comprises an ultrafinecomposite metal particle comprising a core made substantially of a metalcomponent and a covering layer made of an organic substance chemicallybonded to the core.

For manufacturing ultrafine particles made at least partly of a metal,there has been proposed a process of evaporating the metal in a vacuumin the presence of a small amount of a gas to agglomerate ultrafineparticles made of only the metal from the gas phase, producing ultrafinemetal particles. Such a physical process, however, does not lend itselfto mass production as the amount of generated ultrafine metal particlesis small, and is costly because a device for generating an electronbeam, a plasma, or a laser beam, etc. or a device for performinginductive heating is necessary to evaporate the metal. In addition,since the particle diameters range in a wide distribution, some of themetal particles remain unmelted when heated, failing to obtain a uniformmetal film of low resistance.

When ultrafine particles made of only the metal is used, the ultrafineparticles tend to agglomerate in a dispersed liquid, the ultrafineparticle dispersed liquid is liable to provide an irregular coveringlayer. One solution would be to add a suitable surface active agent tothe ultrafine particle dispersed liquid to turn them into a protectivecolloid. However, such a protective colloid fails to provide sufficientdispersion stability.

The bonded structure of ultrafine composite metal particles according tothe present invention appears to be such that a core made of a metalcomponent and an organic compound making up a covering layer share metalmolecules, or an organic compound and a core form a complex-analogousstructure by way of an ionic bond, through the details of the bondedstructure are not clear. Since such ultrafine composite metal particlescan be produced by a chemical process in a liquid phase, they can bemass-produced at a reduced cost in an ordinary atmospheric environmentwith a simple apparatus without the need for a large vacuum device.Since the ultrafine composite metal particles have a uniform diameter,all the ultrafine composite metal particles are fused together at aconstant temperature. Inasmuch as the ultrafine composite metalparticles are covered with an organic metal compound therearound, theirability to agglomerate in a solvent is small, and hence they can easilybe scattered uniformly over the surface of the substrate. The ultrafinecomposite metal particles are stable and hence can easily be handled.Even after the solvent is evaporated, the ultrafine composite metalparticles remain chemically stable until they are decomposed with heatand can be handled for easy process management.

According to a method described in claim 4, in the claim according toany one of claims 1 through 3, the ultrafine particles have an averagediameter ranging from 1 to 20 nm.

It is known that the melting point of a metal particle is lowered as thediameter thereof is reduced. This effect starts to manifest itself whenthe diameter of the metal particle is 20 nm or less, and becomesdistinctive when the diameter of the metal particle is 10 nm or less.Therefore, the average diameter of the ultrafine particles arepreferably in the range from 1 to 20 nm, and preferably in the rangefrom 1 to 10 nm depending on the shape and dimensions of the finerecesses and the structure of the semiconductor device.

According to a method described in claim 5, in the method according toany one of claims 1 through 4, the ultrafine particle dispersed liquidhas a predetermined surface tension to increase adhesiveness of theultrafine particle dispersed liquid to the fine recesses of thesubstrate and/or areas surrounding the fine recesses.

With the ultrafine particle dispersed liquid having a predeterminedsurface tension, the applicability of the ultrafine particle dispersedliquid in the fine recesses of the substrate and on areas surroundingthe fine recesses is increased. Thus, the substrate with a large amountof liquid held thereon can be dried, so that a sufficient amount ofultrafine particles can be supplied to the recesses and the areassurrounding the fine recesses. Consequently, it is not necessary torepeat the applying and drying steps, and the fine recesses can befilled with the metal according to a simple process.

According to an invention described in claim 6, in the method accordingto any one of claims 1 through 5, the step of heating the ultrafineparticles is carried out under the control of an atmosphere. With thisarrangement, an oil mist produced when the ultrafine particles aredecomposed is removed from the substrate surface by a nitrogen gas, forexample. Therefore, the oil mist is prevented from fuming and becomingstagnant on the substrate surface to contaminate the substrate.

According to an invention described in claim 7, in the method accordingto claim 6, the step of heating the substrate is carried out in aninactive gas atmosphere containing a small amount of oxygen or ozone,and thereafter in a pure inactive gas atmosphere. The oxygen or ozoneacts as a catalyst to separate the organic substance and the metal fromeach other, thus promoting the decomposition of the ultrafine particles.For example, when interconnections are to be formed using ultrafineparticles of silver, the ultrafine composite metal particle layer isheated (baked) while a nitrogen gas containing a small amount of oxygenor ozone is flowing, and thereafter a nitrogen gas containing hydrogenis supplied to reduce the silver to form interconnections of purecopper, after which the gas is changed to a nitrogen gas. In thismanner, the interconnections can be formed efficiently.

According to an aspect of the invention, the step of heating thesubstrate is carried out at a temperature of 450° C. or lower. In thismanner, any thermal effect on the semiconductor substrate and circuitsformed thereon can be reduced.

According to another aspect of the invention, there is provided a methodof fabricating a semiconductor wafer by forming an interconnection on asurface of a substrate.

According to a further aspect of the invention, there is provided anapparatus for forming an interconnection, comprising a dispersed liquidsupply device for supplying an ultrafine particle dispersed liquidproduced by dispersing ultrafine particles made at least partly of ametal in a predetermined solvent, to a surface of a substrate havingfine recesses formed therein; and a heat-treating device for heating thesubstrate to melt and bond the metal.

According to still another aspect of the invention, the apparatusfurther comprises a polishing device for chemical mechanical polishingthe surface of the substrate to remove an excessively attached metaltherefrom.

According to still a further aspect of the invention, the dispersedliquid supply device also evaporates the solvent in the ultrafineparticle dispersed liquid supplied to the surface of the substrate.

According to yet another aspect of the invention, the apparatus furthercomprises a supplementary drying device for supplementarily drying thesolvent in the ultrafine particle dispersed liquid supplied to thesurface of the substrate. With this arrangement, it is possible tocompletely dry up an organic solvent which cannot be fully dried up by aspin drying process (air drying process) using a spin coater or thelike, thus preventing voids from being produced in a heating process.

According to yet a further aspect of the invention, the heat-treatingdevice is arranged to heat the substrate under the control of anatmosphere.

According to another option of the invention, the heat-treating devicehas a heating plate which houses a heater for heating the substrate at atemperature of 450° C. or lower and a cooling mechanism.

According to a further option of the invention, the respective devicesare sequentially arranged in an indoor facility along a direction inwhich the substrate moves. With this arrangement, corresponding stepscan successively be performed by the devices in the sequence.

According to yet another option of the invention, the respective devicesare accommodated individually in respective chambers disposed radiallyaround a central transfer chamber with a transfer robot disposedtherein. With this arrangement, corresponding steps can be individuallyperformed and can be combined with each other.

According to yet a further option of the invention, each of theultrafine particles comprises an ultrafine composite metal particlecomprising a core made substantially of a metal component and a coveringlayer made of an organic substance chemically bonded to the core.

According to still another option of the invention, the ultrafineparticles have an average diameter ranging from 1 to 20 nm.

According to still a further option of the invention, there is provideda dispersed liquid supply device for supplying an ultrafine particledispersed liquid produced by dispersing ultrafine particles made atleast partly of a metal in a predetermined solvent, to a surface of asubstrate, comprising: a substrate holder for holding and rotating thesubstrate; a dispersed liquid supply nozzle for dropping the ultrafineparticle dispersed liquid to the surface of the substrate held by thesubstrate holder at a central portion thereof or an area surrounding thecentral portion; a bevel washing nozzle for supplying a washing liquidto a bevel of the substrate held by the substrate holder; and a reverseside washing nozzle for supplying a gas or a washing liquid to thereverse side of the substrate held by the substrate holder.

While the substrate is being rotated, the ultrafine particle dispersedliquid is dropped onto the center of the surface of the substrate touniformly coat the surface of the substrate with the ultrafine particledispersed liquid. At the same time, the bevel washing nozzle suppliesthe washing liquid to the bevel of the substrate to prevent theultrafine particle dispersed liquid from dropping from the edge of thesubstrate and flowing across the edge of the substrate to the reverseside of the substrate. The reverse side washing nozzles also suppliesthe gas or the washing liquid to the reverse side of the substrate toprevent the reverse side of the substrate from being contaminated.

According to another alternative of the present invention, there isprovided a heat-treating device for heating ultrafine particles made atleast partly of a metal to melt and bond the metal, comprising a heatingplate for holding and heating the substrate, and a housing having a gassupply port and a gas discharge port and surrounding a space above thesubstrate held by the heating plate to form a gas chamber between thehousing and the heating plate.

By supplying a predetermined gas into and discharging same from the gaschamber defined between the heating plate and the housing, the ultrafineparticles are heated under the control of an atmosphere so that an oilmist produced when the ultrafine particles are decomposed is removedfrom the substrate surface, and prevented from fuming and becomingstagnant on the substrate surface to contaminate the substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing steps of a method of forming an interconnectionaccording to the present invention;

FIG. 2 is a view schematically showing the structure of a superfineparticle as a material;

FIG. 3 is a view showing steps, which follows the steps shown in FIG. 1,of the method of forming an interconnection according to the presentinvention;

FIG. 4 is a view showing an appearance of an apparatus for forming aninterconnection according to the present invention;

FIG. 5 is a view showing, by way of example, the apparatus for formingan interconnection according to the present invention which is disposedin a clean room;

FIG. 6 is a plan view of the apparatus for forming an interconnectionaccording to the present invention;

FIG. 7 is a perspective view, partly broken away, of a dispersed liquidsupply device of the apparatus for forming an interconnection accordingto the present invention;

FIG. 8 is a vertical sectional front elevational view of the dispersedliquid supply device of the apparatus for forming an interconnectionaccording to the present invention;

FIG. 9 is a cross-sectional view of a supplementary drying device of theapparatus for forming an interconnection according to the presentinvention;

FIG. 10 is a schematic view of a heat-treating device of the apparatusfor forming an interconnection according to the present invention;

FIG. 11 is a vertical sectional front elevational view of theheat-treating device of the apparatus for forming an interconnectionaccording to the present invention;

FIG. 12 is a bottom view of a housing of the heat-treating device of theapparatus for forming an interconnection according to the presentinvention;

FIG. 13 is a plan view of a heating plate of the heat-treating device ofthe apparatus for forming an interconnection according to the presentinvention;

FIG. 14 is a schematic view of a polishing device of the apparatus forforming an interconnection according to the present invention; and

FIG. 15 is a plan view showing the layout of another apparatus forforming an interconnection according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment according to the present invention will be described belowwith reference to the drawings. The embodiment will be used as one typeof a so-called dual-damascene process for forming interconnections ofcopper or silver layers in fine recesses such as interconnectiontrenches defined in the surface of a semiconductor substrate andvertical holes, referred to as contact holes, that interconnect layers.

FIGS. 1A through 1C show successive steps of a method of forming aninterconnection according to the present invention. As shown in FIG. 1A,a semiconductor substrate W includes a semiconductor base 1 with asemiconductor device formed thereon, an electrically conductive layer 1a disposed on the semiconductor base 1, an insulating film 2 of SiO₂deposited on the electrically conductive layer 1 a and having a contacthole 3 and an interconnection trench 4 defined therein by lithographyand etching, and a barrier layer 5 of TaN or the like deposited on thesurface formed so far.

An ultrafine particle dispersed liquid L (see FIG. 1B) is prepared whichcomprises, as shown in FIGS. 2A and 2B, ultrafine composite metalparticles 14 each comprising a core 10 substantially made of a metalcomponent and a covering layer 12 made of an organic compound anddispersed in a given solvent. The ultrafine composite metal particles 14are stable because their cores 10 are covered with the covering layers12 of an organic compound, and have a small tendency to agglomerate inthe solvent.

The ratio of the metal component in the ultrafine composite metalparticles 14 usually ranges from 50 to 90 weight %. For use ininterconnection trenches, the ratio of the metal component in theultrafine composite metal particles 14 is usually in the range from 60to 90 weight %, and preferably in the range from 70 to 90 weight %.

Each of the ultrafine composite metal particles 14 is composed of anorganic compound and a metal component derived from a metal salt as astarting material, e.g., carbonate, formate, or acetate. Each of theultrafine composite metal particles 14 has its central region made ofthe metal component and surrounded by the ionic organic compound. Atthis time, the organic compound and the metal component are chemicallybonded partly or wholly to each other, and exist in integral unity. Theultrafine composite metal particles 14 have high stability and arestable at a higher metal concentration unlike conventional ultrafinemetal particles which are stabilized by being coated with a surfaceactive agent.

The cores 10 of the ultrafine composite metal particles 14 have anaverage diameter which usually ranges from 1 to 20 nm and preferablyfrom 1 to 10 nm.

The ultrafine composite metal particles 14 can be manufactured byheating a metal salt, e.g., carbonate, formate, or acetate, in anonaqueous solvent in the presence of an ionic organic substance at atemperature that is equal to or higher than the decomposition reducingtemperature of the metal salt and also is equal to or lower than thedecomposition temperature of the ionic organic substance.

The metal component comprises at least one of Cu, Ag, Au, Zn, In, Si,Sn, Pd, Fe, Co, Ni, Ru, Rh, Os, Ir, Pt, Cr, Mo, Ba, Bi, Al, W, Ta, Ti,and Pb. The ionic organic substance comprises a fatty acid having acarbon number of 5 or more, an alkylbenzene sulfonic acid, or an alkylsulfonic acid.

The heating temperature is equal to or higher than the decompositionreducing temperature of the metal salt, e.g., carbonate, formate, oracetate, and also is equal to or lower than the decompositiontemperature of the ionic organic substance. For example, if acetate isused as the metal salt, then since its decomposition startingtemperature is 200° C., the metal salt may be kept at a temperature thatis equal to or higher than 200° C. and low enough to keep the ionicorganic substance from being decomposed. To prevent the ionic organicsubstance from being decomposed, the heating atmosphere shouldpreferably be an inactive gas atmosphere. However, the metal salt may beheated in the atmosphere by selecting a nonaqueous solvent.

For heating, various alcohols may be added for accelerating thereaction. Such alcohols are not limited to any particular alcohols, butmay be lauryl alcohol, glycerin, ethylene alcohol, or the like, forexample, insofar as they can accelerate the reaction. The amount of theadded alcohol may be determined depending on the type of the addedalcohol. Usually, the alcohol is added in 5 through 20 parts by weight,preferably 5 through 10 parts by weight, with respect to 100 parts byweight of the metal salt.

After the heating, the ultrafine composite metal particles 14 arerefined according to a known refining process. The refining processincludes a centrifugal separation process, a film refining process, asolvent extracting process, or the like, for example.

The ultrafine composite metal particles 14 thus produced are dispersedin a suitable solvent, producing the ultrafine particle dispersed liquidL. Since the ultrafine composite metal particles 14 as dispersedparticles are very small, the ultrafine particle dispersed liquid L issubstantially transparent when the ultrafine composite metal particles14 are mixed and stirred. Properties of the ultrafine particle dispersedliquid L such as surface tension, viscosity, etc. may be adjusted byappropriately selecting the type of the solvent, the concentration ofthe ultrafine composite metal particles and temperature, etc.

The ultrafine particle dispersed liquid L is dropped onto the substrateW at its center or a spot slightly off the center according to a spincoating process, i.e., while the substrate W is being rotated, forexample. When the ultrafine particle dispersed liquid L has covered thesurface of the substrate W, the dropping of the ultrafine particledispersed liquid L is stopped, thus uniformly coating the entireinterconnection forming surface of the substrate W, as shown in FIG. 1B.In this manner, a liquid film having a given thickness that isdetermined by the viscosity of the ultrafine particle dispersed liquid Land the surface tension acting between the substrate surface and theultrafine particle dispersed liquid L is formed on the substratesurface.

While the ultrafine particle dispersed liquid L is being kept fromdropping, the substrate W is rotated in a spin drying process (airdrying process) to evaporate the solvent in the ultrafine particledispersed liquid L, thus forming an ultrafine composite metal particlelayer 6, which comprises an agglomeration of ultrafine composite metalparticles as a solid material, in the small recesses (the contact hole 3and the interconnection trench 4) and on the substrate surface, as shownin FIG. 1C.

Alternatively, a liquid film having a given thickness may be formed onthe interconnection forming surface of the substrate W by immersing thesubstrate W in the ultrafine particle dispersed liquid L according to adipping process. In this process, undesired areas of the substrate W maybe masked, and the ultrafine particle dispersed liquid L may be stirred,or the ultrafine particle dispersed liquid L or the substrate W may bevibrated in order to fill the small recesses (the contact hole 3 and theinterconnection trench 4) with the ultrafine particle dispersed liquidL.

The process of applying the ultrafine particle dispersed liquid L to theinterconnection forming surface of the substrate W and spin-drying thesubstrate W is repeated a plurality of times as required. The immersingand drying process is put to an end when the small recesses (the contacthole 3 and the interconnection trench 4) are filled to a certain levelwith the ultrafine composite metal particle layer 6. Thereafter, theultrafine composite metal particle layer 6 is decomposed with heat in acontrolled atmosphere by a heating furnace to melt and bond theultrafine composite metal particles together, thus forming a metalinterconnection 7, as shown in FIG. 3B.

Specifically, the ultrafine composite metal particle layer 6 is heatedto 300° C. in 5 minutes, held at 300° C. for 5 minutes, and thereaftercooled to the room temperature in 10 minutes. This heating process isfirst carried out in an inactive gas atmosphere of N₂ or the likecontaining a small amount of oxygen or ozone, and thereafter carried outin a pure inactive gas atmosphere of only N₂ or the like. The oxygen orozone acts as a catalyst to separate the organic substance and the metalfrom each other, thus promoting the decomposition of the ultrafineparticles. An oil mist produced when the ultrafine particles aredecomposed is removed from the substrate surface by the N₂ gas, forexample. Therefore, the oil mist is prevented from fuming and becomingstagnant on the substrate surface to contaminate the substrate.

When interconnections are to be formed using ultrafine particles ofsilver, it is preferable that the ultrafine composite metal particlelayer be heated (baked) while a nitrogen gas containing a small amountof oxygen or ozone is flowing, and thereafter a nitrogen gas containinghydrogen is supplied to prevent the silver from being oxidized andreduce the silver to form interconnections of pure silver, after whichthe gas is changed to a nitrogen gas. In this manner, theinterconnections can be formed efficiently.

By decomposing the ultrafine composite metal particle layer with heat ata temperature of 450° C. or lower, any thermal effect on thesemiconductor substrate and circuits formed thereon can be reduced.

Then, as shown in FIG. 3C, the substrate is chemically and mechanicallypolished to remove the metal and the barrier layer that have beenattached to the substrate surface. Thus, excessive interconnectionfractions are removed. An insulating layer may be formed over the metalinterconnection 7, and a structure as shown in FIG. 1A may be formedagain on the insulating layer, after which the above steps may berepeated to produce a multilayer interconnection structure.

In the above embodiment, ultrafine composite metal particles are used asultrafine particles, and dispersed in a solvent to produce an ultrafineparticle dispersed liquid. However, the ultrafine composite metalparticles may be replaced with generally known ultrafine particles madeof metal only, and those ultrafine particles made of metal only may bedispersed in a solvent to produce an ultrafine particle dispersedliquid. Such a modification is also applicable to an apparatus forforming an interconnection to be described below.

An apparatus for forming an interconnection according to the presentinvention, which is used to carry out the above method of forming aninterconnection, will be described below with reference to FIGS. 4through 15.

FIG. 4 shows a rectangular indoor facility 20 which incorporates anapparatus for forming an interconnection therein. The indoor facility 20has on its ceiling a discharge duct 22 for discharging exhaust gases ina dispersed liquid supply section 44 and a supplementary drying section48, described below, a discharge duct 24 for discharging exhaust gasesin a heat-treating section 52, and an air-conditioning unit 26 forair-conditioning a polishing section 56, etc. The indoor facility 20also has an inlet/outlet port 30 defined in a side wall thereof forintroducing and removing a cassette 28 with substrates W housed thereinand a control panel 32 mounted on the side wall.

As shown in FIG. 5, for example, the indoor facility 20 is disposed in autility zone 34 in a clean room. The indoor facility 20 has an endpositioned in an opening defined in a partition wall 38 which dividesthe utility zone 34 and a clean zone 36 from each other, with theinlet/outlet port 30 and the control panel 32 being exposed in the cleanzone 36. The discharge ducts 22, 24 are connected to a common dischargeduct 25 that extends out of the utility zone 34.

As shown in FIG. 6, the indoor facility 20 has its interior divided intoa loading/unloading section 40 having the inlet/outlet port 30, adispersed liquid supply section 44 housing a dispersed liquid supplydevice 42 therein, a supplementary drying section 48 housing asupplementary drying device 46 therein, a heat-treating section 52housing a heat-treating device 50 therein, and a polishing section 56housing a polishing device 54 therein. These devices 42, 46, 50, 54 arearranged in a sequence along the direction in which the substrate flows,so that a series of interconnection forming steps can successively beperformed on the substrate. The dispersed liquid supply section 44 andthe supplementary drying device 46 are of an explosion-proof structurein view of the explosiveness of an organic solvent.

In the present embodiment, the indoor facility 20 has a singleinlet/outlet port for storing one cassette therein. However, the indoorfacility may have two inlet/outlet ports for storing respectivecassettes therein.

FIGS. 7 and 8 show the dispersed liquid supply device 42 for supplyingthe ultrafine particle dispersed liquid L (see FIG. 1B) to the surfaceof the substrate W. The dispersed liquid supply device 42 comprises asubstrate holder 60 for holding and rotating the substrate W with itsinterconnecting forming surface (face side) oriented upwardly, and abottomed cup-shaped scattering prevention plate 62 surrounding thesubstrate W that is held by the substrate holder 60. The substrateholder 60 has a vacuum chuck on its upper surface for attracting andholding the substrate W, and is connected to the upper end of arotatable shaft 66 that extends from a servomotor 64 for rotation uponenergization of the servomotor 64. The scattering prevention plate 62 ismade of a material resistant to organic solvents, e.g., stainless steel.

A downwardly directed dispersed liquid supply nozzle 68 for dropping theultrafine particle dispersed liquid L is positioned upwardly of eitherthe center of the surface of the substrate W that is held by thesubstrate holder 60 or a spot slightly off the center of the surface ofthe substrate W. The dispersed liquid supply nozzle 68 is connected tothe free end of an arm 70. The arm 70 accommodates therein a pipe forsupplying a metered amount of ultrafine particle dispersed liquid. Thepipe extends from a metered amount supply device 72 such as a syringepump or the like and is communicated with the dispersed liquid supplynozzle 68.

A bevel washing nozzle 74 which is inclined downwardly inwardly ispositioned above the circumferential area of the substrate W held by thesubstrate holder 60, for supplying a washing liquid to the bevel of thesubstrate W. A plurality of reverse side washing nozzles 76 which areinclined upwardly outwardly are positioned below the substrate W held bythe substrate holder 60, for supplying a gas or washing liquid to thereverse side of the substrate W. The scattering prevention plate 62 hasa drain hole 62 a defined in its bottom.

Therefore, the substrate W is held by the substrate holder 60, and theservomotor 64 is energized to rotate the substrate W at a speed rangingfrom 300 to 500 rpm, for example, more preferably from 400 to 500 rpm.While the substrate W is being thus rotated, the dispersed liquid supplynozzle 68 drops a metered amount of ultrafine particle dispersed liquidL onto the central area of the surface of the substrate W. When thesurface of the substrate W is covered with the ultrafine particledispersed liquid L, the dropping of the ultrafine particle dispersedliquid L is stopped so that uniformly coat the surface of the substrateW with the ultrafine particle dispersed liquid L. At the same time, thebevel washing nozzle 74 supplies a hydrophilic organic solvent such asmethanol, acetone, or the like, or a washing liquid such as ethanol,isopropyl alcohol, or the like, to the bevel of the substrate W toprevent the ultrafine particle dispersed liquid L from dropping from theedge of the substrate W or flowing across the edge of the substrate W tothe reverse side of the substrate W. The reverse side washing nozzles 76also supplies a gas such as an N₂ gas, air, or the like, or a washingliquid which is the same as the washing liquid supplied to the bevel ofthe substrate W, to the reverse side of the substrate W to prevent acontamination of the reverse side of the substrate W using the gas flowor the washing liquid.

With the dropping of the ultrafine particle dispersed liquid L beingstopped, the servomotor 4 rotates the substrate W to dry the substrate Win a spin drying process (air drying process) to evaporate the solventin the ultrafine particle dispersed liquid L coated on the substrate W.

The process of applying the ultrafine particle dispersed liquid L to theinterconnection forming surface of the substrate W and spin-drying thesubstrate W is repeated a plurality of times as required. This processis put to an end when the small recesses (the contact hole 3 and theinterconnection trench 4) are filled with a certain level by theultrafine composite metal particle layer 6, i.e., the ultrafinecomposite metal particle layer 6 reaches a certain thickness.

Finally, the substrate may be rotated at a higher speed to quicken thedrying of the solvent. An excessive amount of ultrafine particledispersed liquid L and the washing liquid that has been used to wash thebevel and reverse side of the substrate are discharged out of the drainhole 62 a.

FIG. 9 shows the supplementary drying device 46. The supplementarydrying device 46 has a substrate holding base 80 for holding thesubstrate W with its face side oriented upwardly and a heat-treatingdevice 84 disposed above the substrate holding base 80, theheat-treating device 84 comprising lamp heaters 82, for example.

The supplementary drying device 46 serves to dry up the solvent that hasnot been evaporated by the spin drying process carried out by thedispersed liquid supply device 42. The supplementary drying device 46may not necessarily be required if the solvent is sufficiently dried upby the spin-drying process carried out by the dispersed liquid supplydevice 42 such as when the solvent is coated as a very thin film.

Specifically, if the ultrafine composite metal particle layer 6 (seeFIG. 3A) deposited on the surface of the substrate W is heated while theorganic solvent remains in the ultrafine composite metal particle layer6, voids may possibly be produced at the bottoms of the trenches. Suchvoids are prevented from occurring by completely drying up the solventwith the supplementary drying device 46. The temperature to be achievedby the supplementary drying device 46 is preferably a temperature atwhich the ultrafine particles are not decomposed, e.g., about 100° C.,for thereby preventing a contamination of the supplementary dryingdevice 46 which would otherwise be caused by the decomposition of theultrafine particles.

FIGS. 10 through 13 show the heat-treating device 50 for heating theultrafine composite metal particle layer 6 (see FIG. 3A) to melt andbond the metal together. The heat-treating device 50 has a heating plate90 for holding and heating the substrate W with its face side directedupwardly, a housing 94 which surrounds a space above the substrate Wthat is held by the heating plate 90 to define a gas chamber 92 betweenthe housing 94 and the heating plate 90, and a frame 96 which surroundsthe heating plate 90.

The heating plate 90 is made of aluminum or copper, for example, whichhas a high heat conductivity and can uniformly be heated at a highspeed, and is in the form of a disk. The heating plate 90 houses thereina heater 78 and a temperature sensor 100 for detecting the temperatureof the heating plate 90. The heating plate 90 also has a coolant flowpassage 104 communicating with a coolant inlet passage 103 forintroducing a coolant such as a cooling gas, air, or the like. Thecoolant flow passage 104 communicates with a coolant outlet passage 106.

The housing 94 is made of ceramics, for example, and is fixed to thefree end of a vertically movable arm 108. The housing 94 has a conicalrecess 94 a defined in the reverse side thereof which provides the gaschamber 92 between itself and the substrate W placed on and held by theheating plate 90 when the housing 94 is displaced downwardly.Furthermore, the housing 94 has a gas supply port 94 b defined centrallytherein which is connected to a gas supply pipe 110. The housing 94 alsohas an alternately arranged succession of slits 94 c and pressers 94 don its lower peripheral edge. When the housing 94 is displaceddownwardly, the pressers 94 d are brought into abutment against theperipheral edge of the substrate W that is placed on and held by theheating plate 90, gripping and holing the peripheral edge of thesubstrate W between the heating plate 90 and the pressers 94 d, and theslits 94 c provide gas discharge ports 112.

The frame 96 has a through hole 96 a defined therein which provides agas inlet port 114 with an inner surface thereof. A discharge duct 116communicating with the gas inlet port 114 is fixed to the reverse sideof the frame 96, and is connected to a discharge blower 118.

Therefore, the substrate W is placed on and held by the upper surface ofthe heating plate 90. The substrate W is heated to 300° C. in 5 minutes,for example, held at 300° C. for 5 minutes, and thereafter cooled to theroom temperature in 10 minutes, thus melting and bonding the metal ofultrafine composite metal particles together. At this time, an inactivegas of N₂ or the like containing a small amount of oxygen or ozone isintroduced from the gas supply pipe 110 into the gas chamber 92, andthereafter an inactive gas of only N₂ or the like is introduced from thegas supply pipe 110 into the gas chamber 92. The oxygen or ozone acts asa catalyst to separate the organic substance and the metal from eachother, thus promoting the decomposition of the ultrafine composite metalparticles. An oil mist produced when the ultrafine particles aredecomposed is removed from the substrate surface by the N₂ gas, forexample. Therefore, the oil mist is prevented from fuming and becomingstagnant on the substrate surface to contaminate the substrate.

The oxygen or ozone may be added in a small quantity as it wouldundesirably oxidize the ultrafine particles if added in an excessiveamount.

When interconnections are to be formed using ultrafine particles ofsilver, it is preferable that the ultrafine composite metal particlelayer be heated (baked) while a nitrogen gas containing a small amountof oxygen or ozone is flowing, and thereafter a nitrogen gas containinghydrogen is supplied to prevent the silver from being oxidized andreduce the silver to form interconnections of pure silver, after whichthe gas is changed to a nitrogen gas. In this manner, theinterconnections can be formed efficiently.

FIG. 14 shows the polishing device 54 which chemically and mechanicallypolishes the surface of the substrate W to remove excessively attachedmetal therefrom. The polishing device 54 comprises a polishing table 122with a polishing cloth (polishing pad) 120 attached to its upper surfaceto provide a polishing surface, and a top ring 124 for holding thesubstrate W with its surface to be polished being directed toward thepolishing table 122. The polishing table 122 and the top ring 124 arerotated about their respective own axes. While the polishing cloth 120is being supplied with an abrasive liquid from an abrasive liquid nozzle126 disposed above the polishing table 122, the top ring 124 presses thesubstrate W under a constant pressure against the polishing cloth 120 onthe polishing table 122, thereby polishing the surface of the substrateW. The abrasive liquid supplied from the abrasive liquid nozzle 126comprises, for example, an alkaline solution containing a suspendedabrasive grain which comprises fine particles of silica or the like.Therefore, the substrate W is polished to a flat and mirror finish by achemical and mechanical polishing process based on a combination of achemical polishing action of the alkali and a mechanical polishingaction of the abrasive grain.

When the polishing device 54 continuously performs the polishingprocess, the polishing power of the polishing surface of the polishingcloth 120 is lowered. To recover the polishing power, a dresser 128 isprovided. The polishing cloth 120 is dressed by the dresser 128, forexample, when the substrate W is replaced with another substrate to bepolished. In the dressing process, a dressing surface (dressing member)of the dresser 128 is pressed against the polishing cloth 120 on thepolishing table 122, and the dresser 128 and the polishing table 122 arerotated about their respective own axes to remove the abrasive liquidand abatement attached to the polishing surface, and also to planarizeand dress the polishing surface for thereby regenerate the polishingsurface.

The apparatus for forming an interconnection, thus constructed, operatesas follows: The cassette 28 with substrates W housed therein is placedin the inlet/outlet port 30, and one substrate W is taken out of thecassette 28 and delivered to the dispersed liquid supply device 42 inthe dispersed liquid supply section 44. In the dispersed liquid supplydevice 42, the surface of the substrate W is supplied with the ultrafineparticle dispersed liquid L and then spin-dried, and this process isrepeated a plurality of times as required until the ultrafine compositemetal particle layer 6 (see FIG. 3A) reaches a predetermined thickness.Then, the substrate W is delivered to the supplementary drying device 46in the supplementary drying section 48. In the supplementary dryingdevice 46, the solvent in the ultrafine composite metal particle layer 6is evaporated. Then, the substrate W is delivered to the heat-treatingdevice 46 in the heat-treating section 48. In the heat-treating device46, the ultrafine composite metal particle layer 6 (see FIG. 3A) isheated to melt and bond the metal together, thus forming the metalinterconnection 7 (see FIG. 3B).

The substrate W with the metal interconnection 7 formed thereon is thendelivered to the polishing device 54 in the polishing section 56. In thepolishing device 54, the surface of the substrate W is chemically andmechanically polished to remove excessive metal therefrom. The substrateW is then returned to the cassette 28. The apparatus for forming aninterconnection is capable of successively performing the above steps inthe sequence.

FIG. 15 shows another example of an apparatus for forming aninterconnection. The apparatus comprises a central transfer chamber 132having a transfer robot 130 disposed therein, a dispersed liquid supplychamber 134 housing a dispersed liquid supply device 42 therein, asupplementary drying chamber 136 housing a supplementary drying device46 therein, a heat-treating chamber 138 housing the heat-treating device50 therein, a polishing chamber 140 housing the polishing device 54therein, and plurality of stockyards (temporary placing chambers) 142disposed in given positions between these chambers. The dispersed liquidsupply chamber 134, the supplementary drying chamber 136, theheat-treating chamber 138, the polishing chamber 140, and the stockyards142 are disposed radially around the central transfer chamber 132. Theapparatus also has a second transfer chamber 148 having a mobile robot146 disposed therein, the second transfer chamber 148 being positionedbetween a loading/unloading chamber 144 and the central transfer chamber132.

With the above apparatus for forming an interconnection, the dispersedliquid supply chamber 134 housing the dispersed liquid supply device 42therein, the supplementary drying chamber 136 housing the supplementarydrying device 46 therein, and the other chambers can be constructed asunits. Furthermore, various processes including a dispersed liquidsupply process, a supplementary drying process, etc. can be individuallyperformed and can be combined to carry out a process of forming aninterconnection.

EXAMPLE 1

Oleic acid was used as an organic anionic substance, and silver acetatewas used as a metal source. 0.5 L of a naphthene-based high boilingsolvent having a distilling point of 250° C. was placed into aneggplant-shaped flask having a volume of 1 L, and 10 g of silver acetateand 20 g of oleic acid were added to the solvent. The mixture was thenheated at 240° C. for 3 hours. As the mixture is heated, its colorchanged from colorless to light brown to purple. After the mixture washeated, acetone was added to the mixture, and the mixture was thenrefined by way of precipitation.

The modified powder was observed by a transmissive electron microscope.The observation indicated that the powder was composed of ultrafinemetal particles having a diameter of about 10 nm. An X-ray powderdiffraction process conducted on the powder confirmed cores of metalsilver.

The powder composed of ultrafine metal particles (ultrafine compositemetal particles) was then dispersed in toluene and xylene. Noprecipitation was recognized in either of the solutions, which appearedto be transparent. In other words, the powder was dissolvable.

The dispersion was used as an ultrafine particle dispersed liquid, andcoated on a semiconductor substrate having fine recesses at a ratio of0.05 g per 1 cm². After the semiconductor substrate was dried, it washeated at about 250° C. in a nitrogen atmosphere. The ultrafinecomposite metal particles in the fine recesses were easily melted andsilver interconnections were formed. The silver interconnections weremeasured for their resistance, which was 1.8 μΩ·cm. The semiconductorsubstrate was chemically and mechanically polished using an abrasivegrain of silica, well planarizing the silver interconnections in therecesses without peel-off.

EXAMPLE 2

Stearic acid was used as an organic anionic substance, and coppercarbonate was used as a metal source. 0.5 L of a paraffin-based highboiling solvent having a distilling point of 250° C. was placed into aneggplant-shaped flask having a volume of 1 L, and 10 g of coppercarbonate and 40 g of stearic acid were added to the solvent. Themixture was then heated at 300° C. for 3 hours. As the mixture isheated, its color changed from light green to dark green to brown. Afterthe mixture was heated, methanol was added to the mixture, and themixture was then refined by way of precipitation.

The powder composed of ultrafine metal particles (ultrafine compositemetal particles) was then applied to a substrate in the same manner aswith Example 1. However, the substrate was heated at 300° C. Theultrafine composite metal particles in the fine recesses were easilymelted into copper interconnections. When the substrate was chemicallyand mechanically polished, the copper interconnections were wellplanarized without peel-off.

EXAMPLE 3

Sodium dodecylbenzenesulfonate was used as an organic anionic substance,and gold carbonate was used as a metal source. 0.5 L of xylene (isomermixture) was placed into an eggplant-shaped flask having a volume of 1L, and 5 of gold carbonate and 20 g of sodium dodecylbenzenesulfonatewere added to the solvent. The mixture was then heated at 150° C. for 3hours. As the mixture is heated, its color changed from yellow to lightbrown to red. After the mixture was heated, acetone was added to themixture, and the mixture was then refined by way of precipitation.

The powder composed of ultrafine metal particles (ultrafine compositemetal particles) was then applied to a substrate in the same manner aswith Example 1. However, the substrate was heated at 200° C. Theultrafine composite metal particles in the fine recesses were easilymelted into copper interconnections. When the substrate was chemicallyand mechanically polished, the copper interconnections were wellplanarized without peel-off.

According to the present invention, as described above, it is possibleto stably deposit an interconnection metal of good quality usingultrafine particles which contain the metal at least partly. The processcan be used as a method of forming an interconnection to meetrequirements for highly integrated semiconductor circuits, thuscontributing the progress of a process of fabricating semiconductordevices.

Industrial Applicability

The present invention relates to a method of and an apparatus forforming an interconnection, and more particularly to a method of and anapparatus for forming a fine interconnection in a highly integratedcircuit formed on a semiconductor substrate. According to the presentinvention, the method can be used as a method of forming aninterconnection to meet requirements for highly integrated semiconductorcircuits, thus contributing the progress of a process of fabricatingsemiconductor devices.

What is claimed is:
 1. A method of forming an interconnection,comprising: preparing a substrate having fine recesses formed in asurface thereof; dispersing ultrafine particles in a predeterminedsolvent to produce an ultrafine particle dispersed liquid, wherein theutltrafine particles have a central region made of a metal component andthe central region is surrounded by an organic compound which ischemically bonded to the central region; supplying said ultrafineparticle dispersed liquid to said fine recesses of said substrate;heating said substrate to melt and bond the metal; and chemicalmechanical polishing the surface of the substrate to remove anexcessively attached metal therefrom, wherein said heating comprisesheating said substrate in an inactive gas atmosphere containing a smallamount of oxygen or ozone, and then heating said substrate in a pureinactive gas atmosphere.
 2. A method according to claim 1, furthercomprising: evaporating said solvent after said supplying said ultrafineparticle dispersed liquid to said fine recesses of said substrate andbefore said heating said substrate to melt and bond the metal.
 3. Amethod according to claim 1 or 2, wherein said covering layer made of anorganic substance chemically bonded to said core comprises an ionicorganic compound.
 4. The method of claim 3, wherein said ionic organiccompound is selected from the group consisting of a fatty acid havingcarbon number of at least 6, an alkylbenzene sulfonic acid, and an alkylsulfonic acid.
 5. A method according to claim 1, wherein said ultrafineparticles have an average diameter ranging from 1 to 20 nm.
 6. A methodaccording to claim 1, wherein said ultrafine particle dispersed liquidhas a predetermined surface tension to increase adhesiveness of saidultrafine particle dispersed liquid to said fine recesses of saidsubstrate and/or areas surrounding said fine recesses.
 7. A methodaccording to claim 1, wherein said heating said ultrafine particles iscarried out under the control of an atmosphere.
 8. A method according toclaim 7 or 1, wherein said heating said substrate is carried out at atemperature of 450° C. or lower.
 9. A method of fabricating asemiconductor wafer by forming an interconnection on a surface of asubstrate using a method according to claim 1.